I've been looking at my airlock, and an hour ago it would bubble every 1.5 seconds, half hour ago it would bubble every 1 second, and now its rolling at every .5 seconds.

Just cooked up the batch today, but its my second time brewing, and I'm wondering what the warning signs are that you might need some more fermcap?

Wait until the bubbles roll every .3 seconds. Once they do, take note of the time and jot it down on a piece of paper. Put the paper in your pocket and go outside. Outside, begin to dance beneath the sky for 8 to 12 minutes. Then, return to the airlock and sit before in, lotus style. You must stare at the bubbles until it begins rolling every .28 seconds and only then can you start chanting the sacred brew texts. If you do that, you might be ok. Otherwise please, forget about it.